Not Applicable.
Not Applicable.
The present invention relates to the general field of antenna carriers and more particularly to a structure for housing and carrying an antenna with reduced sensitivity to external interferences, especially from the human hand. The structure may be a portable receiver such as a smart card or chip card.
U.S. Pat. No. 5,844,244 sets out an example of a portable receiver. Such receivers are often referred to as electronic tickets. A second example is set out in WO 98/26370. Herein, a wireless communication system with portable receivers is described wherein the data transfer occurs via a magnetic H-field. Frequencies of 6.78 Mz or 27 MHz are typically effective. If transmitters of the above mentioned frequency are placed within the entrance area of a door, the transmitted electromagnetic field in the entrance area is developed as a near-field. The expression near-field means that the so-called H-portion dominates. The section of the near-field is generally defied by the character r for which the relationship r less than 0.6xc2x7xcex applied. xcex refers to wavelength. For xcex=22 m, at a frequency of for example 13.5 MHz, the near-field conditions are fulfilled at up to a distance of approximately 12 m.
The transmission via frequencies at above the mentioned examples would require large antennas with dimensions of several meters. However, the maximum size of the antenna is given or limited by the size of the device or carrier element. The receiver antenna has to be reduced for example to the dimensions of a chip card for contactless detection systems. Such chip cards generally have measurements approximate to a standard credit card which is 53xc3x9785 mm2. Such a high reduction of the antenna size leads to a very low antenna reciever voltage on the one hand and to an increased sensitivity of the antenna voltage to the surroundings on the other. The low sensitivity can be mostly compensated for by an appropriate pre-stage amplification. However, with chip cards it is to be noted that the power consumption of such pre-stages has to be as low as possible. Furthermore, the antenna voltage is reversed proportional to the third power of the ratio of the receiver antenna distancexe2x80x94transmitter antenna in the near-field section. The number of turns of such antennas is very limited due to space limitations.
Additionally, there is the problem with portable receivers, that the reception is disturbed by, for example, the human hand or other electrically conducting bodies located nearby. The interference can cause, for example, a severely reduced antenna voltage or a detuning of the antenna. A changing of the provided frequency of resonance is described by detuning. Because changes may result from received power with transmitted information, a particularly reliable transmission is required.
An advantage of the present invention is a carrier element for an antenna with reduced sensitivity to interfering influences from its"" surroundings. These and other advantages are effected by an apparatus comprising: at least one antenna winding, said winding running in a layer of said element, at least one shield divided into parts by at least one partition, said shield running above and parallel to said layer, said parts being electrically insulated from one another. In the apparatus said at least one shield comprises at least a second shield, said second shield being divided in second parts by at least one second partition, said second parts being electrically insulated from one another. The apparatus may further comprise a third shield disposed atop said first shield and second shield, said third shield including at least one third partition dividing said third shield into third parts, said third parts being electrically insulated from one another.